1. Field of the Invention
The present invention relates to a filter disposed in the interior of a burner portion of a gas lighter to adjust the flow rate of gas and a method for producing same.
2. Description of the Prior Art
Gas lighters are provided with an adjusting valve for adjusting the flow rate of gas. Particularly, in conventional disposable plastic gas lighters, the said adjusting valve is constructed so that LPG (liquefied petroleum gas) as fuel permeates into a filter such as a urethane foam filter which is compressed to an appropriate extent. And the flow rate of gas is adjusted by adjusting the compression ratio of the filter.
However, in such a filter as a urethane foam filter, not only an average pore diameter is relatively large, but also the scatter in pore diameters is large, so the flame length is not constant. Further, there occur changes in the flame length because of poor chemicals resistance against LPG, etc.
For the purpose of solving this problem, for example U.S. Pat. No. 4,101,262 proposes the use of a microporous membrane formed of polypropylene as the filter material. This microporous membrane, having a pore diameter of about 0.1.about.1 .mu.m.times.0.01 .mu.m.times.0.1 .mu.m and a thickness of 20.about.30 .mu.m, is said to exhibit a molecular sieve effect such that when fuel containing n-butane as a main component or fuel containing isobutane as a main component is used, only a vaporized portion of liquefied gas is allowed to pass through the membrane, while the liquid portion is not allowed to pass through the membrane.
As to chemicals resistance against LPG, etc., the polypropylene filter is superior to conventional urethane foam filters, but in the use over a long period its chemicals resistance is not considered satisfactory.
Further, the polypropylene filter is required to be as thin as 20 to 30 .mu.m in order to retain its function as a molecular sieve. Consequently, the handling thereof is inconvenient, and when it is incorporated in a lighter mechanism, the number of parts and that of assembling steps increase, resulting in increase of the cost.
Additionally, although this can be said of conventional filters at large, not limited to polypropylene filters, there easily occurs a spitting phenomenon in which liquefied gas flows in a liquid state out of the filter. This is presumed to be because of insufficient supply of vaporization heat at the time of vaporization of the liquefied gas. Upon occurrence of such spitting phenomenon, the flame length pulsates, and particularly a large pulsation between long and short flames is dangerous.
On the other hand, sintered metals are extremely good in chemicals resistance. However, when a sintered metal filter is press-fitted in a lighter at the time of incorporating the filter into a lighter, the pores of the filter will be crushed by the resulting compressive force, resulting in deterioration or scatter in the gas transmitting function. There is the problem of gradual increase in flame length during use of the filter. This may be because a too high thermal conductivity promotes the vaporization of LPG. Further, sintered metals having pores not larger than 2.0 .mu.m which size is suitable for the function as a filter are difficult to be obtained probably because the metal particles are easily fused to each other. This is also one of the causes of obstructing the practical application of sintered metal filters.